GROWTH AND INVIVO DIGESTIBILITY IN CATTLE FED GRASS HAY TREATED WITH UREA AND SODIUM-HYDROXIDE, ALONE OR IN COMBINATION

The nutritive value of mature grass hay, alkali-treated at harvesting, was examined. The herbage was either not treated (C) or sprayed immediately before cutting with NaOH (S; 500 g/l, 24 g/kg forage dry matter (DM)). After wilting for 3 days, half of C and S was baled without further treatment while half was treated with solid urea (U; 16 g/kg DM). The bales were sealed under polythene for 8 months. The DM concentration (g/kg) and concentrations (g/kg DM) of N, neutral detergent fibre (NDF) and digestible DM for treatments C, U, S and SU were 784, 785, 762 and 668 (s.e.d. 32), 19.8, 23.5, 18.0 and 20.9 (s.e.d. 0.58), 720, 689, 707 and 676 (se.d. 7.81) and 507, 599, 576 and 663 (s.e.d. 20), respectively. The hays were offered ad libitum to four Friesian steers in a Latin square experiment to determine in vivo digestibility (IVD). Daily DM intake of C, U, S and SU were 6.41, 7.43, 7.62 and 7.73 (s.ed. 0.28) kg DM, respectively. The corresponding IVD values were: DM 491, 531, 544 and 568 (s.e.d. 23), NDF 637, 661, 688 and 700 (s.e.d. 25) and acid detergent fibre (ADF) 497, 500, 587 and 592 (s.e.d. 51). The hays were also offered ad libitum with 2 kg concentrates per head daily to 48 Hereford x heifers in a randomised complete block experiment for 86 (control and urea-treated hays) or 115 (NaOH-treated hays) days prior to slaughter. Daily liveweight gains (g), daily carcass gains (g) and killing-out proportions (g/kg) were 793, 944, 952 and 979 (s.e.d. 64), 348, 446, 471 and 491 (s.e.d. 35) and 488, 493, 499 and 500 (s.e.d. 5.5) for C, U, S and SU, respectively. It is concluded that treatment with urea and NaOH as described can improve the nutritive value of poor quality hay.